A New Way To Remove Contaminants From Storm Water

The new method uses naturally abundant materials to remove dissolved substances from rainwater.

Researchers coated the sand with manganese oxide, making it more biodegradable.

Urban storm water contains low concentrations of trace organic contaminants obtained from automobile wear, biocides, asphalt, and consumer products, which could be harmful to both ecosystem and human health. Municipal wastewater effluent consists of organic compounds (such as urban use pesticides, personal care products, and pharmaceuticals) at same concentrations.

Afraid of pollutants and toxic chemicals present in the storm water that runs across herbicide-soaked lawns and past overflowing sewers, several cities try their best to divert this water into rivers and streams.

In order to provide an inexpensive and efficient way of removing contaminants from water, researchers at the University of California, Berkeley have developed a new technique, which involves coating the sand with manganese oxide and bathing it in a solution of low-concentrated chlorine. It will purify the storm water percolating into underground aquifers, forming a safe reservoir of drinkable water for parched communities.

As rainwater rushes over streets, lawns, and roofs, it can collect plenty of dangerous chemicals, including toxic metals, vehicle oil, pesticides, herbicides, and even poop. When a city gets a lot of excess rain, it discharges this polluted water into local rivers and streams.

Diverting rainwater into underground aquifers through sand could be the best solution for water-strapped cities like Los Angeles. Aquifers can be used to store water (like big rain barrels) during intense rainfall until it’s required in the dry season. However, the quality of water has become a big issue.

The new method uses naturally abundant materials to remove several contaminants that pose serious risks to underground water systems. Although the engineered sand cannot remove all kinds of contaminants, it could be used along with other purification approaches to remove numerous harmful contaminants picked up by water.

The Chemistry

The coated sand is made by mixing plain sand with 2 variants of manganese that react to produce manganese oxide. It’s a non-toxic mineral that mixes with other organic chemicals like pesticides, herbicides, and endocrine-disrupting bisphenol-A (BPA), breaking them into tinier chunks that are more biodegradable.

Although manganese oxides were identified in soils 4 decades ago, this is the first time scientists have engineered it in a useful manner. The dull-brown sand coated with manganese oxide has unique properties that are safe and nature-friendly.

The team tested their technique by percolating simulated rainwater (containing low-concentrated BPA) through material’s columns. Initially, the engineered sand was able to remove almost all BPA, but its effectiveness degraded over a specific period of time.

To ‘recharge’ the capabilities of manganese oxide, they put the sand in a low-concentrated chlorine solution. This helped them restore all initial reactivity of the manganese oxide, without having to dig up the sand and replace it every year or two. More specifically, 25 parts per million of chlorine in water takes nearly 2 days to recharge 0.5-meter deep layer of sand.

Future and Applications

The study explains mineralogy-reactivity relationships and how the structure of manganese oxide changes during redox reactions. Although this research focuses on rainwater infiltration applications, the geomedia can have other applications as well, such as controlled aquifer recharge with municipal wastewater effluent, agricultural runoff, and advanced wastewater treatment.

Researchers plan to perform field tests in Sonoma County using local creek’s rainwater. They believe that this technique would lead to geomedia with a longer lifetime that is cheaper to utilize and regenerate.